Physics
Electromagnetic Energy
Electromagnetic energy refers to the energy carried by electromagnetic waves, which include visible light, radio waves, microwaves, and X-rays. These waves are created by the movement of electrically charged particles and can travel through a vacuum. Electromagnetic energy plays a fundamental role in various natural phenomena and technological applications.
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11 Key excerpts on "Electromagnetic Energy"
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter- 5 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Learning Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter- 6 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenol-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ____________________ WORLD TECHNOLOGIES ____________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Library Press(Publisher)
____________________ WORLD TECHNOLOGIES ____________________ Chapter 6 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenomenon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ____________________ WORLD TECHNOLOGIES ____________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 6 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a phenol-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
No longer available |Learn more- (Author)
- 2014(Publication Date)
- Academic Studio(Publisher)
________________________ WORLD TECHNOLOGIES ________________________ Chapter 5 Electromagnetic Radiation Electromagnetic radiation (often abbreviated E-M radiation or EMR ) is a pheno-menon that takes the form of self-propagating waves in a vacuum or in matter. It comprises electric and magnetic field components, which oscillate in phase perpendicular to each other and perpendicular to the direction of energy propagation. Electromagnetic radiation is classified into several types according to the frequency of its wave; these types include (in order of increasing frequency and decreasing wavelength): radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays and gamma rays. A small and somewhat variable window of frequencies is sensed by the eyes of various organisms; this is what is called the visible spectrum. The photon is the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation and is also the force carrier for the electromagnetic force. EM radiation carries energy and momentum that may be imparted to matter with which it interacts. ________________________ WORLD TECHNOLOGIES ________________________ Physics Theory Shows three electromagnetic modes (blue, green and red) with a distance scale in micrometres along the x-axis. Electromagnetic waves were first postulated by James Clerk Maxwell and subsequently confirmed by Heinrich Hertz. Maxwell derived a wave form of the electric and magnetic equations, revealing the wave-like nature of electric and magnetic fields, and their symmetry. Because the speed of EM waves predicted by the wave equation coincided with the measured speed of light, Maxwell concluded that light itself is an EM wave. According to Maxwell's equations, a spatially-varying electric field generates a time-varying magnetic field and vice versa .
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
24.1 | The Nature of Electromagnetic Waves In Section 13.3 we saw that energy is transported to us from the sun via a class of waves known as electromagnetic waves. This class includes the familiar visible, ultraviolet, and infrared waves. In Sections 18.6, 21.1, and 21.2 we studied the concepts of electric and magnetic fields. It was the great Scottish physicist James Clerk Maxwell (1831–1879) who showed that these two fields fluctuating together can form a propagating electromagnetic wave. We will now bring together our knowledge of electric and magnetic fields in order to understand this important type of wave. Figure 24.1 illustrates one way to create an electromagnetic wave. The setup con- sists of two straight metal wires that are connected to the terminals of an ac generator and serve as an antenna. The potential difference between the terminals changes sinus- oidally with time t and has a period T. Part a shows the instant t 5 0 s, when there is no charge at the ends of either wire. Since there is no charge, there is no electric field at the point P just to the right of the antenna. As time passes, the top wire becomes positively charged and the bottom wire negatively charged. One-quarter of a cycle later ( t 5 1 4 T ), the charges have attained their maximum values, as part b of the drawing indicates. The corresponding electric field E B at point P is represented by the red arrow and has increased to its maximum strength in the downward direction.* Part b also shows that the electric field created at earlier times (see the black arrow in the picture) has not dis- appeared but has moved to the right. Here lies the crux of the matter: At distant points, the electric field of the charges is not felt immediately. Instead, the field is created first near the wires and then, like the effect of a pebble dropped into a pond, moves outward as a wave in all directions. Only the field moving to the right is shown in the picture for the sake of clarity.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler(Authors)
- 2021(Publication Date)
- Wiley(Publisher)
Reproduced with permission. 780 CHAPTER 24 Electromagnetic Waves Concept Summary 24.1 The Nature of Electromagnetic Waves An electromag- netic wave consists of mutually perpendicular and oscillating elec- tric and magnetic fields. The wave is a transverse wave, since the fields are perpendicular to the direction in which the wave travels. Electromagnetic waves can travel through a vacuum or a material substance. All electromagnetic waves travel through a vacuum at the same speed, which is known as the speed of light c (c = 3.00 × 10 8 m/s). 24.2 The Electromagnetic Spectrum The frequency f and wavelength λ of an electromagnetic wave in a vacuum are related to its speed c through the relation c = fλ. The series of electromagnetic waves, arranged in order of their frequencies or wavelengths, is called the electromagnetic spectrum. In increasing order of frequency (decreasing order of wavelength), the spectrum includes radio waves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays. Visible light has fre- quencies between about 4.0 × 10 14 and 7.9 × 10 14 Hz. The human eye and brain perceive different frequencies or wavelengths as different colors. 24.3 The Speed of Light James Clerk Maxwell showed that the speed of light in a vacuum is given by Equation 24.1, where 0 is the (electric) permittivity of free space and μ 0 is the (magnetic) perme- ability of free space. c = 1 ______ √ ____ 0 μ 0 (24.1) 24.4 The Energy Carried by Electromagnetic Waves The total energy density u of an electromagnetic wave is the total energy per unit volume of the wave and, in a vacuum, is given by Equation 24.2a, where E and B, respectively, are the magnitudes of the electric and magnetic fields of the wave. Since the electric and magnetic parts of the total energy density are equal, Equations 24.2b and 24.2c are equivalent to Equation 24.2a. In a vacuum, E and B are related accord- ing to Equation 24.3.
eBook - PDF- E. C. Pielou(Author)
- 2008(Publication Date)
- University of Chicago Press(Publisher)
Science will always be incomplete. There is no reason to believe that humans as a species have the capacity to understand everything there is to understand or that our thoughts provide anything more profound than mental images. That said, we return to EM waves—what they are, how they are generated, and how their energy is dissipated. The Nature of Electromagnetic Waves As we saw in chapter 16, a magnetic field appears spontaneously in the neigh-borhood of an electric current; and a current flows spontaneously in a conduc-198 c h a p t e r e i g h t e e n tor moving through a magnetic field. Recall, too, that a current consists of moving electric charges, and moving charges create moving electric fields. Putting these facts together, we realize that moving electric fields create mag-netic fields and vice versa: moving magnetic fields create electric fields. The processes are symmetrical. And because the two kinds of fields are absolutely dependent on each other, they can be thought of jointly as the two components of a single electromagnetic field. Electromagnetic waves are moving “disturbances” in an electromagnetic field, caused when moving electrons accelerate or decelerate. Consider what would happen if you caused an electric field to oscillate or, what comes to the same thing, vibrate. Bear in mind that an electric field has both a direction (see fig. 16.3) and a magnitude or strength, and the same goes for a magnetic field. An oscillating field is one whose strength grows from zero to a maximum pointing in one direction, say to the right, then dwindles to zero again, then grows to the same maximum pointing to the left, then dwindles to zero again, then ... And so on. It never stops accelerating, either to the left or to the right. Now imagine that an electric field starts to oscillate; its coupled magnetic field is forced to oscillate too. The magnetic field’s strength grows and dwindles in time with the electric field’s, but at right angles to it.
eBook - PDFPhysics of Thermal Therapy
Fundamentals and Clinical Applications
- Eduardo Moros(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
57 4.1 Introduction The use of Electromagnetic Energy to cause heating and/or abla-tion of biological tissue is widespread as evidenced in other chapters in this book. To understand and optimize the use of such energy sources it is necessary to consider some fundamen-tal aspects of the electromagnetic spectrum (see Figure 4.1). We shall be interested in nonionizing electromagnetic fields for which the photon energy, given by the product of the fre-quency and Planck’s constant ( = 6.626 × 10 − 34 Js), is insufficient to cause ionization. In particular we shall discuss aspects of interactions between the body and electromagnetic fields such as microwaves (MW) and radiofrequency (RF) fields. The term RF is often used in the biological effects and medical applica-tions literature to cover the ranges from 3 kHz to 300 GHz, respectively. The frequency range from 300 MHz to 300 GHz is also referred to as the “microwave range.” The consensus of sci-entific opinion is that interactions between such fields and the human body are thermal, and although there have been claims for other mechanisms of interaction, the plausibility of the vari-ous nonthermal mechanisms that have been proposed is very low (ICNIRP, 2009). 4.2 Static Electric and Magnetic Fields Electric and magnetic fields are produced by electric charges and their motion. Electric charge may be positive or negative. The force F e between two charged spherical bodies whose radii are small compared to the distance between them, r , and which are remote from other dielectric media is F e = 1 4 πε r q q r 1 2 2 (4.1) where q 1 and q 2 are the charges and ε is the permittivity of the medium in which they are located. In free space ε = ε 0 = 8.854 × 10 − 12 F m − 1 . Bold typeface indicates a vector quantity.
eBook - PDF- John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler, Heath Jones, Matthew Collins, John Daicopoulos, Boris Blankleider(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
24.2 Calculate speed, frequency, and wavelength for electromagnetic waves. The frequency f and wavelength of an electromagnetic wave in a vacuum are related to its speed c through the relation c = f. The series of electromagnetic waves, arranged in order of their frequencies or wavelengths, is called the electromagnetic spectrum. In increasing order of frequency (decreasing order of wavelength), the spectrum includes radio waves, infrared radiation, visible light, ultraviolet radiation, X‐rays, and gamma rays. Visible light has frequencies between about 4.0 × 10 14 and 7.9 × 10 14 Hz. The human eye and brain perceive different frequencies or wavelengths as different colours. 24.3 Relate the speed of light to electromagnetic quantities. James Clerk Maxwell showed that the speed of light in a vacuum is given by equation 24.1, where 0 is the (electric) permittivity of free space and 0 is the (magnetic) permeability of free space. c = 1 √ 0 0 (24.1) 24.4 Calculate energy, power, and intensity for electromagnetic waves. The total energy density u of an electromagnetic wave is the total energy per unit volume of the wave and, in a vacuum, is given by equation 24.2a, where E and B, respectively, are the magnitudes of the electric and magnetic fields of the wave. Since the electric and magnetic parts of the total energy density are equal, equations 24.2b and 24.2c are equivalent to equation 24.2a. In a vacuum, E and B are related according to equation 24.3. u = 1 2 0 E 2 + 1 2 0 B 2 (24.2a) u = 0 E 2 (24.2b) u = 1 0 B 2 (24.2c) E = cB (24.3) Equations 24.2a–24.2c can be used to determine the average total energy density, if the rms average values E rms and B rms are used in place of the symbols E and B. The rms values are related to the peak values E 0 and B 0 in the usual way, as shown in equations 1 and 2. The intensity of an electromagnetic wave is the power that the wave carries perpendicularly through a surface divided by the area of the surface.
eBook - PDF- H.R. Everett(Author)
- 1995(Publication Date)
- A K Peters/CRC Press(Publisher)
The optical portion of the electromagnetic spectrum encompasses wavelengths from 0.012 micron (ultraviolet) up to 1000 microns (infrared); the infrared region can be further subdivided into near-infrared, mid-infrared, and far-infrared (adapted from Banner, 1993, and Buschling, 1994). The infrared portion of the electromagnetic spectrum encompasses wavelengths of 0.72 to 1,000 microns. All objects with an absolute temperature above 0°K emit radiant energy in accordance with the Stephan-Boltzman equation (Buschling, 1994): W = e g T where: W = emitted energy 8 = emissivity a = Stephan-Boltzman constant (5.67 x 10'12 watts/cm2K4) T = absolute temperature of object in degrees Kelvin. Chapter 9 Electromagnetic Energy 253 The totality of all energy incident upon an object surface is either absorbed, reflected, or reradiated in accordance with Kirchoff s law. Emissivity (e) is defined as the ratio of radiant energy emitted by a given source to that emitted by a perfect blackbody radiator of the same area at the same temperature under identical conditions (Graf, 1974). Emissivity is also a convenient measure of energy absorption. A hypothetical surface with an emissivity value of zero is a perfect reflector, neither absorbing nor emitting radiant energy, whereas in contrast, a theoretical blackbody with an ideal emissivity of one would absorb 100 percent of the supplied energy, reflecting none (Buschling, 1994). 9.1.1 Electro-Optical Sources In 1977 the IEEE redefined a radar as “an electromagnetic means for target location and tracking” (IEEE, 1977). As pointed out by Sundaram (1979), this includes electro-optical devices such as laser radars (lidars) or laser rangefinders in general. Relative to microwave and millimeter-wave systems, electro-optical sensors are characterized by extremely short wavelengths affording much higher resolution, but suffer the greatest attenuation by atmospheric constituents.
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